The invention relates to an optical information recording medium and, more particularly, to an optical information recording medium which can read out or read/write at a high recording density and has high reliability for the repetitive recording and reproducing operations.
In an optical information recording medium, a compact disc (CD), a laser disc (LD), or the like has been widespread. In recent years, a DVD having a recording density that is seven or more times as large as that of the CD has been put into practical use. As for the DVD, development is being made as a rewritable recording/reproducing medium besides a read only ROM (DVD-ROM) in which information has directly been written on a board. The realization of the practical use of the DVD is being examined also as an RAM for a computer (DVD-RAM).
In a DVD, a high density recording has been accomplished by using a laser beam having a shorter wavelength of about 650 nm than that of the laser (780 nm) used in a CD or the like. In order to handle information of a large capacity such as computer graphics or the like, however, it is necessary to accomplish a further high recording density that is 1.5 to 2 times as large as the above density. To accomplish it, development of semiconductor lasers of green to blue of further short wavelengths (wavelengths: 520 to 410 nm) is being made.
A super resolution film can be mentioned as another high recording density technique. The super resolution film is a film which is formed on a lower surface of a recording medium and a high recording density can be accomplished by reducing a beam spot of incident light transmitted through the film.
One of mechanisms of a super resolution effect is a satural absorption phenomenon which is a phenomenon realized by using such nonlinear optical characteristics that the super resolution film transmits light having an intensity that is equal to or larger than its satural absorption amount and absorbs light having an intensity below the satural absorption amount. Since a spatial intensity of the laser beam which is used for reading or writing has a Gaussian distribution, when the beam passes through the super resolution film, the light at a bottom portion having a low intensity is absorbed by the super resolution film and the light at a center portion having a high intensity is transmitted. Therefore, a beam diameter after the transmission can be reduced.
At present, as such a super resolution film, an organic film of the phthalocyanine system, materials (compounds) of the chalcogenide system, or the like as shown in JP-A-8-96412 or the like can be mentioned. Besides them, such a trial that, as the same organic material, a thermochromic material disclosed in JP-A-6-162564 or a photochromic material disclosed in JP-A-6-267078 is used as a super resolution film is also known.
However, each of the materials as mentioned above has problems in terms of the reliability, productivity, and the like. In the organic film, since an energy density of the beam is locally very high upon recording or reading, if the recording or reproducing operation is repetitively performed, there is a fear that the film deteriorates gradually. Therefore, it is difficult to guarantee the sufficient number of times of the recording or reproducing operation under a severe use environment as in case of an RAM for a computer or the like. Since chalcogenide is chemically unstable, it is difficult to obtain a long guaranteeing period.
It is an object of the invention to obtain an optical recording medium having a super resolution film which can guarantee the repetitive recording or reproducing operation for a long period and has high productivity and a high super resolution effect.
To solve the above problem, according to the invention, there is provided an optical information recording medium comprising, at least: a board on which pits having information have been formed; and a film which is formed directly on the board or formed thereon through another layer and changes a reflectance or an intensity distribution of reflection light in dependence on an intensity of incident light (such a film is hereinbelow also referred to as a super resolution film), wherein the film is inorganic materials (compounds) constructed by N (N=2, 3, 4, . . . : integer of 2 or more) kinds of phases, the phases in a range from at least one kind to (Nxe2x88x921) kinds among the N kinds of phases are continuous phases, and the other phases are discontinuous phases.
The discontinuous phases are, for example, phases such as spherical or pillar fine particles and are phases having such a discontinuous structure that they are distributed in one matrix. The continuous phases are phases represented by such a matrix phase and are phases all of which are continuous and exist not being independent. The continuous phases exist so as to disperse the discontinuous phases.
There is also provided an optical information recording medium comprising, at least: a board; a film which is formed directly on the board or formed thereon through another layer and changes a reflectance or an intensity distribution of reflection light in dependence on an intensity of incident light; and a recording film which is formed directly on the film or formed thereon through another layer and on which information is recorded by the light, wherein the film is inorganic materials (compounds) constructed by N (N=2, 3, 4, . . . : integer of 2 or more) kinds of phases, the phases in a range from at least one kind to (Nxe2x88x921) kinds among the N kinds of phases are continuous phases, and the other phases are discontinuous phases. A mean diameter of the discontinuous phases lies within a range from 1 nm or more to 70 nm or less. A width of continuous phases existing between the discontinuous phases lies within a range from 0.3 nm or more to 100 nm or less. Further, the continuous phases are amorphous inorganic compounds and the discontinuous phases are crystal inorganic compounds. The continuous phases are a dielectric substance and the discontinuous phases are any of a metal, a semiconductor, and a dielectric substance.
According to the invention, there is provided an optical information recording medium comprising, at least: a board on which pits having information have been formed; and a film which is formed directly on the board or formed thereon through another layer and changes a reflectance or an intensity distribution of reflection light in dependence on an intensity of incident light, wherein the film is constructed by N (N=2, 3, 4, . . . : integer of 2 or more) kinds of phases containing at least one or more kinds of elements selected from Co, Ti, V, Cr, Mn, Fe, Ni, Si, Pb, Bi, and Al, the phases in a range from at least one kind to (Nxe2x88x921) kinds among the N kinds of phases are continuous phases, and the other phases are discontinuous phases.
Further, there is provided an optical information recording medium comprising, at least: a board; a film which is formed directly on the board or formed thereon through another layer and changes a reflectance or an intensity distribution of reflection light in dependence on an intensity of incident light; and a recording film which is formed directly on the film or formed thereon through another layer and on which information is recorded by the light, wherein the film is constructed by N (N=2, 3, 4, . . . integer of 2 or more) kinds of phases containing at least one or more kinds of elements selected from Co, Ti, V, Cr, Mn, Fe, Ni, Si, Pb, Bi, and Al, the phases in a range from at least one kind to (Nxe2x88x921) kinds among the N kinds of phases are continuous phases, and the other phases are discontinuous phases.
Further, according to the invention, there is provided an optical information recording medium comprising, at least: a board; a film which is formed directly on the board or formed thereon through another layer and changes a reflectance or an intensity distribution of reflection light in dependence on an intensity of incident light; and a recording film which is formed directly on the film or formed thereon through another layer and on which information is recorded by the light, wherein a refractive index of the film changes due to the incident light when the incident light enters, and assuming that a refractive index at the time when no incident light enters is labelled to n0 and an intensity of the incident light is set to I, if the absolute value n of the refractive index that is measured is indicated by
n=n0+n2I
a value of n2 lies within a range from 1.0xc3x9710xe2x88x929 (m2/W) or larger to 1.0xc3x9710xe2x88x927 (m2/W) or less.
In this instance, the refractive index change (nxe2x88x92n0) occurs in such a manner that the refractive index is saturated within a period of time which lies within a range from 2.50xc3x9710xe2x88x927 second or longer to 3.50xc3x9710xe2x88x927 second or shorter after the irradiation of the incident light and is recovered to the original refractive index within a time interval which lies within a range from 2.5xc3x9710xe2x88x927 second or longer to 1.0xc3x9710xe2x88x922 second or shorter after the removal of the incident light.
Further, the film is an oxide which contains a Co oxide of 60 to 95 weight % as an oxide of CoO and in which a remaining part is constructed by elements of at least one or more kinds among Si, Ti, Al, Pb, and Bi.
According to the invention, there is provided an optical information recording/reproducing apparatus comprising, at least: lasers of a plurality of wave-lengths; means for selecting one of the lasers; and a mechanism for automatically adjusting a focal point which changes every laser, wherein the apparatus further has means for discriminating a recording capacity of a medium to record or reproduce and means for changing a tracking in accordance with the medium discriminated by the discriminating means.